This invention relates to a motor vehicle with a tank for transporting fluids and is directed to means to eliminate the safety hazard of operating the motor vehicle while the tank is connected with a source for replacement. While the invention is broadly applicable for its purpose, it is being initially applied to a tank truck for transporting a liquid petroleum gas such as butane under relatively high pressure.
The loading facility has a supply line extending from the bulk storage tank line. A loading hose, which generally varies in length from ten to twenty feet, is permanently attached at one end to the supply line. Tank trucks which stop to receive a supply of butane from a loading facility ordinarily have a filler valve for each tank to be loaded. A loading hose is mechanically connected to each filler valve by means of a nozzle on the free end of the hose which mates with the filler valve in a positive manner, for instance by screw threads. There are at least two on/off valves to permit flow of the butane. One is located near the bulk storage tank, and the other is located downstream from the filler valve. A third on/off valve would exist if the tank truck has twin barreled tanks with a filler valve on each, and would be located downstream of the second filler valve. The tank truck's operator connects the loading hose and the filler valve and then turns all on/off valves on. When the tanks are filled, the on/off valves are turned off and the loading hose then disconnected. A potential hazard evolves if the tank truck's operator attempts to drive off while the loading hose and the filler valve(s) are still connected. Under the best circumstances, the on/off valves would have been turned off while the loading hose was still connected. This might result in damage to the truck tank or to the loading hose, or it might result in ruptured piping to create a leak. Under the worst circumstances, the on/off valves would be left in the on position while the loading hose was still connected. The combination of a highly inflammable, pressurized fluid with a running engine, whereby a hot exhaust or spark could ignite the fluid and result in a violent explosion and/or intense fire, could be catastrophic.
U.S. Pat. No. 2,847,023 discloses means to immobilize a tank truck or to prevent operation of a tank truck as long as any such hose connection exists for either delivery from or replenishment of the truck's tank. The safety system is actuated by either removal of the delivery hose nozzle from its normal transportation position on the truck or by change to the operative state of the refill inlets; actuation results in application of the vehicle's wheel brakes to prevent operation of the truck. The system has several disadvantages. The number of parts increases the probability of parts failure. Location of parts makes access for repair more difficult. An added independent act is required, i.e., manual operation of a release valve to permit release of the rear wheel brakes, before the tank truck can be restarted. If the actuating plunger fails to retract sufficiently to place the brake line from the brake pedal in communication with the rear brakes, the operator of the tank truck may only have use of the front wheel brakes, a true driving hazard. Also, the second form of the invention (see FIG. 3) has no means provided for prevention of accidental ignition caused by the operation of electrical equipment in a highly hazardous atmosphere (i.e., use of three switches, a solenoid, and control circuits around butane). Electrical equipment which yields sparks and/or arcs during the operative state, e.g., switches and circuit breakers, can, when used in close proximity to or in conjunction with flammable gases or combustible dusts, cause ignition if there is a suitable mixture with air. Heat producing devices, such as the aforementioned motors, are problematic, as are parts of the electrical equipment which experience insulation failure, e.g., solenoids and wiring. Therefore, the utmost care must be exercised when using electrical devices and wiring around hazardous gases and vapors such as butane and gasoline. With further reference to the second form of the invention (and FIG. 3), an electrical fault in the wiring circuit would prevent actuation of the system, and the tank truck could be driven off while the loading hose is still connected.
U.S. Pat. No. 2,002,757 discloses a system which precludes the possibility of dispensing liquid when the motor of the truck is in operation. A pressure operated electrical switch is incorporated in conjunction with the ignition circuit for the motor truck engine, and this switch is so associated with the hydraulic valve system that when the actuator is operated to effect opening of one of the valve units, the ignition circuit of the engine is rendered inoperative. Thus, operation of the truck is precluded when the valve units are open. However, when the valve units are closed the truck can be driven off, even though the hose is still connected. Also, there is no mention of protection during loading of the tanks.
The present invention safely overcomes these hazards and disadvantages in an economical, simplistic, and fail-safe fashion.